The present invention relates to a car navigation system which measures a current position of a vehicle, displays a map and the current position on the map on a display screen, and guides a passenger or driver of the vehicle to a target position.
As a prior art system for reliably guiding a vehicle to a target position along a route, a car navigation system is known. In an example of the prior art, for the purpose of displaying the vicinity of the current position of the vehicle (equipped with the system), the vicinity of the target position, or the vicinity of a guiding intersection in an easy-to-understand manner, there is proposed a system which displays a map in a three-dimensional manner (refer to, e.g., JP-A-2001-273526).
In a car navigation system disclosed in the above JP-A-2001-273526, structures on a road map in a bird's eye view are displayed three-dimensionally. As an example, buildings located within a predetermined distance from the current position of a vehicle are displayed as reduced or enlarged so that ones of the buildings closer to the current position of the vehicle are reduced to avoid the closer buildings from being hidden by other buildings; whereas, ones of the buildings located further from the current vehicle position are magnified for an easy-to-see purpose, thus improving the visibility of the three-dimensionally displayed map.
As another example of the prior art car navigation systems, there is proposed a car navigation system which can display as magnified the vicinity of the current position and can display a wide range of road map from the current position to target position (refer to JP-A-2002-206928).
The invention disclosed in the above JP-A-2002-206928 displays a road map in a bird's eye view. That is, the map is like viewed from above the vicinity of the current position of the vehicle in a vehicle heading direction or in a direction toward the target position. Thus the user can always grasp the situations of the vehicle running direction. At this time, flag marks are given to the current and target positions. And when the target position is out of the displayable range of the bird's eye view, a flag mark is attached to a position in the displayable range of the bird's eye view which is located in a direction toward the target position and is closer to the target position, enabling the driver to always grasp the current situations of a route toward the target position. In such a bird's eye view, further, a place located farther from the current position of the vehicle is given in the upper side of the display screen on a small scale, while the vicinity of the current position of the vehicle is given in the lower side of the display screen on a large scale. Thus, when all data (road data, title data, background data, etc.) are to be displayed in the bird's eye view, the quantity of data to be displayed becomes too much to be displayed in the upper side of the display screen of the small scale and covering a large area of the map. For this reason, priority order is applied to such data so that data including information having low priorities are displayed in the lower side of the display screen, while only data having high priorities are displayed in the upper side thereof.
In the car navigation system of the aforementioned JP-A-2001-273526, even such a building as to be actually hidden by its user-side building can be displayed and can be easily searched for. Meanwhile, even a building located at a further distance can be noticeably displayed as magnified and thus can be easily searched for. However, when the car runs in an area having many structures or in an area having many tangled roads crossing each other, many structures are displayed, which results in that the user cannot easily find a desired drop-in place in the many-structure area. In particular, in a city or town having many high-rise buildings, even when the driver wants to drop in at a desired restaurant or parking lot, such an area usually has many low buildings, so such a low building often tends to be hidden by another high building and cannot be displayed.
In the invention of the aforementioned JP-A-2002-206928, on the other hand, when a road map is displayed in a bird's eye view, the map is displayed two-dimensionally, so that even a restaurant, an area such as a parking lot or title data is displayed simultaneously. Thus such a desired area can be searched for from the road map. In the invention of the above JP-A-2002-206928, however, road data, title data or background data having a large scale and a low priority is displayed simultaneously. As a result, roads are displayed as intersected and tangled and many facilities are also displayed together with their titles, thus resulting in highly complicated display. For this reason, it is highly difficult to search for a restaurant or parking lot which is usually not a target position but at which the driver just wants to drop in. Further, when the driver wants to drop in at such a place after the vehicle runs by a certain distance, and even when the bird's eye view is displayed, it is impossible to display and find the place which has a low priority and is located away by a certain distance or more.
As mentioned above, prior art car navigation systems including the above two car navigation systems for guiding a vehicle up to a passenger's or driver's desired position (target position) along a running route have had a problem which follows. That is, when the driver wants to drop in at a restaurant or parking lot as necessary on the way to the target position, the driver must troublesomely search the displayed three-dimensional map or bird's eye view map for the desired drop-in place.
Such a car navigation system is usually designed to receive traffic information about a traffic jam caused by an accident, a road construction or the like. However, when the car navigation system receives such traffic information, the passenger or driver must troublesomely determine whether to run the vehicle along the guided route or to find a detour by himself. Thus when the driver have a poor knowledge of a road network in the vicinity, he has to inevitably run the vehicle along the congested route.
The aforementioned conventional car navigation system has another problem. That is, when the driver run the vehicle in an area such as a city or town having tangled roads crossing each other, a road map is displayed showing the tangled roads as they are, and the driver cannot sometimes find a running route easily. In particular, in the case of an intersection having a right or left turn, the driver has a hard time to find the intersection because the displayed road map has too much information.
In this way, the conventional car navigation systems including the above two car navigation systems also have a problem. That is, when a special situation takes place during the running of the vehicle along the route, no suitable, easy-to-understand guidance is given to the driver.